Linear guide assembly

ABSTRACT

Three rows of ball rolling grooves  23 A to  23 C are formed in each side of a guide rail  21,  while being vertically arrayed. Three rows of ball rolling grooves  25 A to  25 C are also formed on the inner surface of each of the legs of a slider  22.  The ball rolling grooves  25 A to  25 C are respectively disposed in opposition to the ball rolling grooves  23 A to  23 C to thereby form ball sliding passages  26 A to  26 C. In either of the upper or lower ball rolling passage  26 A or  26 C, each ball contacts, at four points, with the surfaces of the ball rolling groove  23 A or  23 C of the guide rail  21  and the ball rolling groove  25 A or  25 C of the slider  22.  In the remaining ball rolling passages, each ball contacts at two points with the surfaces of the ball rolling grooves. One of lines L 1  and L 4,  each of which connects two opposite contact points of those four ones in the upper or lower ball rolling passage is oriented in the same direction as of lines L 2  and L 3  connecting the contact points in the remaining ball rolling passages. With such a construction, the upper, medium and lower rows of ball trains receive all loads acting on the slider in share, whereby the linear guide assembly exhibits its maximum load capacity against the loads.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to the improvement of the loadcapability and rigidity of a linear guide assembly which receives loadsthrough a number of balls which circulate, while rolling, in ballrolling passages extending through the guide rail and the sliderslidable on the guide rail.

[0002] An example of this type of the linear guide assembly is disclosedin a Japanese Utility Model Examined Publication No. Hei. 6-646. In thedisclosed linear guide assembly, at least three rows of ball rollinggrooves, or upper, medium and lower ball rolling grooves, are formed ineach side of a guide rail. A slider, which is slidable on the guiderail, has legs extending along both sides of the guide rail. Each of thelegs of the slider includes ball rolling grooves respectively disposedin opposition to the ball rolling grooves of the guide rail, and ballcirculating passages parallel to the ball rolling grooves thereof. Anumber of balls are put in the ball circulating passages. With movementof the slider, the balls circulate through the ball circulating passageswhile rolling therein. As shown in FIGS. 1(a) and 1(b), each of balls Bcontacts, at two points (T1 and T2), with the surface of a ball rollinggroove of a guide rail 1 and the surface of a ball rolling groove of aslider 2, which is disposed so as to face the corresponding ball rollinggroove of the guide rail 1. Prolonged lines L1 to L3 each connecting thecontact points T1 and T2 are converged at intersection points O1 and O2,located inside the guide rail 1.

[0003] Another conventional linear guide assembly of the same type isdisclosed in a Japanese Utility Model Unexamined Publication No. Sho.64-53622. As shown in FIGS. 2(a) and 2(b), the linear guide assembly hasalso a three-row ball rolling groove structure. In the passages definedby the upper and lower ball rolling grooves of the slider and the guiderail, which are confronted with each other, each ball contacts, at twopoints T1 and T2, with the surfaces of its associated ball rollinggrooves being confronted with each other. In the passage defined by themedium ball rolling grooves facing each other, each ball contacts, atfour points T1 to T4, with the surfaces of the ball rolling grooves ofthe guide rail and the slider.

[0004] When the intersection points (converging points) of the prolongedlines connecting the contact points of the balls with the groovesurfaces are located inside the guide rail, an elastic displacement ofthe linear guide assembly is increased against a moment load acting onthe slider so as to roll the slider, and the linear guide assemblyexhibits an self-aligning function. On the other hand, when theconverging points are located outside the guide rail, the linear guideassembly exhibits a high rigidity against the moment load.

[0005] In the Japanese Utility Model Examiner Publication No. Hei. 6-646shown in FIGS. 1(a) and 1(b), its load capacity is limited to a loadcapacity corresponding to only two rows of ball rolling grooves. Thereason for this is that when a load F acts on the upper side of theslider 2 (FIG. 1(a)) or a load f acts on the lower side thereof (FIG.1(b)), the load is received by one or two rows of ball rolling grooves.

[0006] The load capacity of the Japanese Utility Model UnexaminedPublication No. Sho. 64-53622, as shown in FIG. 2(a), is limited to thatcorresponding to two rows of the ball rolling grooves as of the JapaneseUtility Model Examiner Publication No. Hei. 6-646 shown in FIGS. 1(a)and 1(b). The linear guide assembly may be constructed such that theload is received by the upper, medium and lower ball rolling grooves, asshown in FIG. 2(b). In this case, the intersection points O1 and O2 ofthe prolonged lines L1 to L3 connecting the contact points T1 to T4 arelocated separately inside and outside the guide rail 1, and theself-aligning function fails to operate and the rigidity against themoment load is low. In this respect, this is impractical.

[0007] Further, in an actual use of the linear guide assembly, theupward and downward loads acting on the linear guide assembly aregenerally different in their magnitudes. To increase the rigidity of thelinear guide assembly against an excessively load acting thereon, ameasure may be taken in which an increased pressure is merely applied inadvance to the linear guide assembly may be made. However, the measureresults in an excessive increase of the prepressure, possibly leading tothe damage of the linear guide assembly.

[0008] In the Japanese Utility Model Unexamined Publication No. Sho.64-53622, there is no description on a ratio of the radius of curvatureof the flank of the groove of the ball rolling passage to the diameterof the ball (the ratio will be referred to as a groove R ratio),although the linear guide assembly of the publication is unique in thatthe ball contacts at four points with the groove surfaces in the mediumball rolling passage, and the ball contacts at two points with thegroove surfaces in the upper and lower ball rolling passages.Incidently, in the conventional linear guide assembly, referred toabove, which has two rows of ball rolling passages, the groove R ratiosof the two rows of ball rolling passages are equal. The conventionallinear guide assembly having three rows of ball rolling passages has notyet been put into practice. In designing this linear guide assembly forits actual use, the structure of the linear guide assembly having tworows of ball rolling passages will be directly applied to the linearguide assembly.

[0009] The load capacity and rigidity of the linear guide assemblybecome large with increase of the contact area of the ball and the ballrolling passage. To increase the load capacity and rigidity at a fixedball size, it is only needed to reduce the radius of curvature of theflank of the ball rolling passage.

[0010]FIG. 3 is a diagram showing the relationship between the groove Rratios and contact angles of the flanks of the ball rolling grooves,which define the ball rolling passages in which each ball contacts withthe groove surfaces at two points. In the ball rolling passage shown inFIG. 3(a), the flank f of the ball rolling groove Ma has the radius ofcurvature R1. In the ball rolling passage shown in FIG. 3(b), the flankf of the ball rolling groove Mb has the radius of curvature R2. Here,R1>R2. Since the radius of curvature is small (a groove R ratio of theradius of curvature of the flank f to the diameter of the ball 210 issmall), a contact area Sb, elliptical in shape, of the ball rollinggroove Mb where it contacts with the ball 210 may be larger than acontact area Sa, elliptical in shape, of the ball rolling groove Ma(Sb>Sa). If the contact area is large, the load capacity and rigidity ofthe linear guide assembly are increased. The reason why the contact areais elliptical is that the ball rolling grooves Ma and Mb are linear inthe direction vertical to the paper of the drawing.

[0011] The relationship between the groove R ratios (the radii ofcurvature) and contact angles of the flanks of the ball rolling grooves,which define the ball rolling passage in which each ball contacts withthe groove surfaces at four points, will be described with reference toFIG. 4. In FIG. 4, for ease of explanation, the curvature radii R1 andR2 of the right and left flanks fL and fR of a Gothic arch groove Mg aredifferent from each other; R1 (left)>R2 (right). Let an initial contactangle θ be 45° for both the flanks fL and fR (flanks indicated byone-dot chain lines). In this case, the center of the curvature of theleft flank fL is O1, and that of the right flank fR is O2.

[0012] The curvature centers O1 and O2 of the flanks fL and fR aredisplaced to positions O1′ and O2′, respectively. For a change quantityα of the contact angle θ of the ball 210, a change quantity α1 of thecontact angle of the ball on the right flank having the curvature radiusR2 is much greater than a change quantity α2 of the contact angle on theleft flank having the curvature radius R1, although the displacementquantities (offset values) A1 and A2 of the curvature centers are equalto each other.

[0013] Thus, in the ball rolling passage having four contact points,contact conditions of the ball and the ball rolling grooves are easy tochange, so that basic characteristics of the linear guide assembly, suchas load capacity, rigidity and rolling frictional force, also change.

[0014] Where the radius of curvature of the ball rolling groove of theball rolling passage having four contact points is small, a small errorof the contact angle of the ball on the ball rolling groove greatlyaffects the function and characteristics of the linear guide assembly.For this reason, the accuracy control in working the product isdifficult. Where four contact points are used and the radius ofcurvature is small, the contact area is large and the slide is great.Where the radius of curvature of the ball rolling groove of the ballrolling passage having four contact points is large, the load capacityand the rigidity of the resultant linear guide assembly are inunsatisfactory levels. Thus, a designer encounters an antinomic problemin designing the linear guide assembly.

SUMMARY OF THE INVENTION

[0015] Accordingly, an object of a first aspect of the present inventionis to solve the above-mentioned problem of the conventional liner guideassembly, particularly to provide a linear guide assembly having thefollowing advantages: When the slider receives a load (F) acting on theupper side thereof as to press it against the guide rail or a load (f)acting on the lower side thereof as to move it apart from the guiderail, the upper, medium and lower ball rolling grooves receive the loadin share. When a moment acts at a right angle to the lengthwisedirection of the guide rail, the linear guide assembly exhibits a highrigidity against the moment load When a mounting error is created inassembling the linear guide assembly, the linear guide assemblyexercises the self-aligning function to absorb the error, if it iswithin a tolerable range.

[0016] To achieve the above object, there is provided a linear guideassembly according to the first aspect of the present invention, inwhich a slider is mounted on a guide rail having three rows of ballrolling grooves on each side thereof, three rows of ball circulatingpassages are formed in each of two legs of the slider which extend aboveand along both the sides of the slider, a number of balls being put inthe ball circulating passages, each of the ball circulating passageincluding a ball rolling groove disposed facing the corresponding ballrolling groove of the guide rail, the opposed ball rolling groovesforming a first ball rolling passage, a ball return or second passageparallel to the ball rolling passage, and curved passages, one of thecurved passages interconnecting the first ends of the first and secondball rolling passages, while the other interconnecting the second endsof the first and second ball rolling passages,

[0017] wherein

[0018] 1) in the upper or lower load ball rolling passage, each ballcontacts, at four points, with the surfaces of the ball rolling groovesof the guide rail and the slider, while in the remaining two ballrolling passages, each ball contacts, at two points, with the surfacesof the ball rolling grooves of the guide rail and the slider, and

[0019] 2) intersection points of one of lines each connecting the twoopposite contact points of those four contact points of the upper orlower ball rolling passages, and lines connecting respectively the twoopposite contact points of the remaining two ball rolling passages arelocated inside or outside the guide rail.

[0020] In the linear guide assembly thus constructed, the prolongedlines, each of which connects the contact points of each ball where theball contacts with the surfaces of the ball rolling grooves therein, areoriented in the same directions. Therefore, all loads acting on theslider are received in share by three rows of ball trains within thethree upper, medium and lower ball rolling passages. Therefore, thelinear guide assembly exhibits its maximum load capacity against theload.

[0021] The prolonged lines, each of which connects the contact points ofeach ball where the ball contacts with the groove surfaces, converge atpoints located inside or outside the guide rail. Therefore, when thelinear guide assembly receives a turning effect (moment load) in thedirection orthogonal to the lengthwise direction of the guide rail, thelinear guide assembly exhibits a high rigidity or an self-aligningfunction.

[0022] For the above background reasons, a second aspect of the presentinvention is made and has an object to provide a linear guide assemblyhaving three rows of ball rolling passages which is capable ofsatisfying the requirements of high load capacity and high rigidity, andselecting such a load capacity as not to increase a ball rollingresistance in accordance with the direction of the load applied to thesliding block by such a unique technical idea that two or three rows ofball rolling passages receive a load acting on the assembly, and thenumber of the rows of ball rolling passages used is selected inaccordance with the direction of the load applied.

[0023] To achieve the above object, there is provided a linear guideassembly according to the second aspect of the present invention, inwhich a sliding block is mounted on a guide rail having three rows ofball rolling grooves on each side thereof, three rows of ballcirculating passages are formed in each of two legs of the sliding blockwhich extend above and along both the sides of the sliding block, anumber of balls being put in the ball circulating passages, each of theball circulating passage including a ball rolling groove disposed facingthe corresponding ball rolling groove of the guide rail, the opposedball rolling grooves forming a first ball rolling passage, a ball returnor second passage parallel to the ball rolling passage, and curvedpassages, one of the curved passages interconnecting the first ends ofthe first and second ball rolling passages, while the otherinterconnecting the second ends of the first and second ball rollingpassages,

[0024] in which in at least two ball circulating passages, each the ballcontacts, at four points, with the surfaces of the ball rolling groovesof the guide rail and the sliding block.

[0025] In the linear guide assembly thus constructed, in all the ballcirculating passages, each ball contacts, at four points, with thesurfaces of the ball rolling grooves. Therefore, the linear guideassembly receives a load applied to the sliding block through the ballson the ball rolling grooves of the ball circulating passages. Therefore,the linear guide assembly exhibits its maximum load capacity and highrigidity to the load applied thereto, independently of the direction ofthe load.

[0026] In at least two ball circulating passages, each ball contacts, atfour points, with the surfaces of the ball rolling grooves, whereby thelinear guide assembly exhibits its maximum load capacity and highrigidity against the load acting thereon in every direction. Theremaining ball circulating passage is arranged such that each balltherein contacts at two points with the surfaces of the ball rollinggrooves, in consideration with the direction of the load acting on thesliding block. The linear guide assembly thus constructed receives theload by at least two rows of balls. In a direction where the load islarge, the linear guide assembly receives the load by three rows ofballs. Therefore, the load capacity and rigidity of the linear guideassembly may be selected to be as large as possible so long as therolling resistance is not increased.

[0027] In addition, an object of a third aspect of the present inventionis to provide a linear guide assembly which are improved in its loadcapacity and rigidity without reducing the radius of curvature of theball rolling grooves contacting with the ball at four contact points, orwhile keeping easy accuracy control, and without little increasingrolling friction of balls. The present invention is based on thefollowing facts:

[0028] 1) The load capacity and rigidity are increased where the radiusof curvature of the two-contact-point groove is smaller than that of thefour-contact-point groove.

[0029] 2) The two-contact-point groove is originally low in rollingfriction. Therefore, even if the radius of curvature of the groove isreduced, an increase of the rolling friction is not great.

[0030] To achieve the above object, a linear guide assembly according tothe third aspect of the present invention in which a sliding block ismounted on a guide rail having three rows of ball rolling grooves oneach side thereof, three rows of ball circulating passages are formed ineach of two legs of the sliding block which extend above and along boththe sides of the sliding block, a number of balls being put in the ballcirculating passages, each of the ball circulating passage including aball rolling groove disposed facing the corresponding ball rollinggroove of the guide rail, the opposed ball rolling grooves forming afirst ball rolling passage, a ball return or second passage parallel tothe ball rolling passage, and curved passages, one of the curvedpassages interconnecting the first ends of the first and second ballrolling passages, while the other interconnecting the second ends of thefirst and second ball rolling passages,

[0031] wherein

[0032] 1) of three rows of the first ball rolling passages, at least onerow of the first ball rolling passage is arranged such that each ballcontacts, at four points, with the groove surfaces, while the remainingrows of the first ball rolling passages are arranged such that each ballcontacts, at two points, with the groove surfaces,

[0033] 2) a groove R ratio of the flanks of the ball rolling grooves ofeach of the first ball rolling passages where each ball contacts at twopoints with the groove surfaces, is more than 50% but smaller than thatof the flanks of the ball rolling grooves of the first ball rollingpassage where each ball contacts at four points with the groovesurfaces.

[0034] The above mentioned construction may be modified such that agroove R ratio of the flanks of the ball rolling grooves of each of thefirst ball rolling passages where each ball contacts at two points withthe groove surfaces, is more than 50% but less than 53%, and a groove Rratio of the flanks of the ball rolling grooves of the first ballrolling passage where each ball contacts at four points with the groovesurfaces, is between 53% and 56%.

[0035] In the construction according to the third aspect of the presentinvention, of the three rows of ball rolling passages formed on eachside of the linear guide assembly, only one row of ball rolling passageis arranged such that each ball contacts, at four contact points, withthe groove surfaces. The remaining two ball rolling passages arearranged such that each ball contacts, at two points, with the groovesurfaces. In the ball rolling passages of the two contact points, therolling friction of the ball is low, and even if the radius of curvatureof the groove is small, the rolling friction of the ball is increasednot so much. A groove R ratio of the groove of each of those ballrolling passages of the two contact points is set to be smaller than ofthe ball rolling passage of the four contact points. Thus, the radius ofcurvature of the groove of the four-contact-point ball rolling passageremains as intact, but the radius of curvature of the groove of eachtwo-contact-point ball rolling passage, the working of which isrelatively easy and its working little affects the rolling friction, isreduced. As a result, the load capacity and rigidity are increased witha little increasing of the rolling friction. The groove R ratio of eachtwo-contact-point ball rolling passage is set at more than 50%. Thereason for this is that at 50% of the groove R ratio, the size (radius)of the ball is equal to that of the ball rolling groove, and the entirerange of the flank when viewed in the radial direction comes in contactwith the ball, to thereby provide a maximum contact area.

[0036] In the modification of the above-mentioned construction accordingto the third aspect of the present invention, the groove R ratio of eachtwo-contact-point ball rolling passage is set to be more than 50% butless than 53%. The reason for this is that if the groove R ratio is notmore than 50%, the radius of curvature of the groove is below the radiusof the ball, viz., such a groove is nonsense, and if it exceeds 53%, itis impossible to secure the required load capacity and rigidity.

[0037] As for the four-contact-point ball rolling passage, if its grooveR ratio is less than 53%, the contact area is excessively large, therolling friction is noticeable, and the working of grooves and itsaccuracy control are difficult. If the groove R ratio exceeds 56%, it isimpossible to secure the load capacity and rigidity in excess of thoseof the conventional four-contact-point ball rolling passage.

[0038] In the linear guide assembly of the invention, the groove R ratioof the ball rolling groove of the four-contact-point ball rollingpassage is used as intact, viz., it is set at a value approximatelyequal to that of the ball rolling groove of the two-contact-point ballrolling passage, so as not to make it difficult to work the grooves andto control the accuracy in the working of the grooves. The groove Rratio of the ball rolling groove of the two-contact-point ball rollingpassage, in which the rolling friction of the ball is originally low, isset at a value smaller than of the conventional one. Therefore, the loadcapacity and rigidity can successfully be increased while keeping easyworking of grooves and easy control of working accuracy and littleincreasing the rolling friction of the balls.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a view useful in explaining how a load acting on aslider of a conventional linear guide assembly is shared by the balls,where a load in FIG. 1(a) is a compression load, and a load in FIG. 1(b)is a tension load;

[0040]FIG. 2 is a view useful in explaining how a load acting on aslider of another conventional linear guide assembly is shared by theballs, where a load in FIG. 2(a) is a compression load, and a load inFIG. 2(b) is a tension load;

[0041]FIG. 3 is a diagram showing the relationship between the groove Rratios and contact angles of the flanks of the ball rolling grooves,which define the ball rolling passages in which each ball contacts withthe groove surfaces at two points;

[0042]FIG. 4 is a diagram showing the relationship between the groove Rratios and contact angles of the flanks of the ball rolling grooves,which define the ball rolling passage in which each ball contacts withthe groove surfaces at four points;

[0043]FIG. 5 is a front view of a linear guide assembly according to afirst embodiment of the present invention, in which the half of the endcap is removed;

[0044]FIG. 6 is a cross sectional view taken on line VI-VI in FIG. 5;

[0045]FIG. 7 is an enlarged view typically showing one of load ballrolling passages;

[0046]FIG. 8(a) is an engaged view showing a key portion of a linearguide assembly according to a second embodiment of the presentinvention, and FIG. 8(b) is a view useful in explaining how a loadacting on a slider of the assembly is shared by the balls;

[0047]FIG. 9(a) is an engaged view showing a key portion of a linearguide assembly according to a third embodiment of the present invention,and FIG. 9(b) is a view useful in explaining how a load acting on aslider of the assembly is shared by the balls;

[0048]FIG. 10(a) is an engaged view showing a key portion of a linearguide assembly according to a fourth embodiment of the presentinvention, and FIG. 10(b) is a view useful in explaining how a loadacting on a slider of the assembly is shared by the balls;

[0049]FIG. 11 is a view useful in explaining how a turning/rollingmoment acting on the slider of the linear guide assembly of the fourthembodiment is shared by the balls;

[0050]FIG. 12 is a view useful in explaining how a turning/rollingmoment acting on the slider of the linear guide assembly of the thirdembodiment is shared by the balls;

[0051]FIG. 13 is a front view of a linear guide assembly according to afifth embodiment of the present invention, a portion of which is cutout;

[0052]FIG. 14 is a cross sectional view taken on line XIV-XIV in FIG.13;

[0053]FIG. 15 is an enlarged view showing a key portion of the linearguide assembly of FIG. 13, in which how the balls in three rows of ballrolling passages receive a compression load applied to a sliding blockin share is diagrammatically illustrated;

[0054]FIG. 16 is an enlarged view showing a key portion of the linearguide assembly of FIG. 13, in which how the balls in three rows of ballrolling passages receive a tensile load applied to the sliding block inshare is diagrammatically illustrated;

[0055]FIG. 17 is a front view of a linear guide assembly according to asixth embodiment of the present invention, a portion of which is cutout;

[0056]FIG. 18 is an enlarged view showing a key portion of the linearguide assembly of FIG. 17, in which how the balls in three rows of ballrolling passages receive a compression load applied to a sliding blockin share is diagrammatically illustrated;

[0057]FIG. 19 is a front view of a linear guide assembly according to aseventh embodiment of the present invention, a portion of which is cutout;

[0058]FIG. 20 is an enlarged view showing a key portion of the linearguide assembly of FIG. 19, in which how the balls in three rows of ballrolling passages receive a tensile load applied to a sliding block inshare is diagrammatically illustrated;

[0059]FIG. 21 is a front view of a linear guide assembly according to aeighth embodiment of the present invention, a portion of which is cutout;

[0060]FIG. 22 is an enlarged view showing a key portion of the linearguide assembly of FIG. 21, in which how the balls in three rows of ballrolling passages receive a compression load applied to a sliding blockin share is diagrammatically illustrated;

[0061]FIG. 23 is an enlarged view showing a key portion of amodification of the linear guide assembly of FIG. 22, in which how theballs in three rows of ball rolling passages receive a compression loadapplied to a sliding block in share is diagrammatically illustrated;

[0062]FIG. 24 is a side view of a linear guide assembly according to aninth embodiment of the present invention, in which the right side ofthe end cap is removed;

[0063]FIG. 25 is a cross sectional view taken on line XXV-XXV in FIG.24; and

[0064]FIG. 26 is an enlarged view typically showing one of load ballrolling passages.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] The preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

[0066] FIGS. 5 to 7 cooperatively show a linear guide assembly accordingto a first embodiment of the present invention. FIG. 5 is a front viewof the linear guide assembly in which the right half of the end cap isremoved. FIG. 6 is a cross sectional view taken on line VI-VI in FIG. 5.FIG. 7 is an enlarged view typically showing one of load ball rollingpassages. The construction of the linear guide assembly will first bedescribed. As shown, a slider 22, U-shaped in cross section, is putabove a guide rail 21 such that the guide rail 21 and the slider 22 moverelative to each other. Three rows of ball rolling grooves, that is,upper, medium and lower ball rolling grooves 23A, 23B and 23C, whilelongitudinally extending, are formed in each side of the guide rail 21.Each of the ball rolling grooves is shaped like a pointed arch, called aGothic arch, having two centers and equal curvatures. Relief grooves 33,34 and 35, which are provided for ball holders H, are formed in thebottoms of the ball rolling grooves 23A, 23B and 23C, respectively.

[0067] Ball rolling grooves 25A, 25B and 25C, while being verticallyarrayed, are formed in the inner surface of each of the legs 24 of ablock body 22A of the slider 22. The ball rolling groove 25A is disposedin opposition to the upper ball rolling groove 23A of the guide rail tothereby form a ball sliding passage 26A; The ball rolling groove 25B isdisposed in opposition to the medium ball rolling groove 23B to therebyform a ball sliding passage 26B; The ball rolling groove 25C is disposedin opposition to the lower ball rolling groove 23C to thereby form aball sliding passage 26C. Ball return passages 27A, 27B and 27C,substantially circular in cross section, are formed in the thick part ofeach of the legs 24 of the block body 22A, while being verticallyarrayed and extending lengthwise, and respectively parallel to the ballrolling passages 26A, 26B and 26C.

[0068] Three rows of halved-doughnut shaped, curved passages, or upper,medium and lower curved passages 29A, 29B and 29C, are formed in each ofend caps 28 that are applied to the front and rear ends of the blockbody 22A. The upper curved passage 29A interconnects the ball rollingpassage 26A and the ball return passage 27A; The medium curved passage29B interconnects the ball rolling passage 26B and the ball returnpassage 27B; The lower curved passage 29C interconnects the ball rollingpassage 26C and the ball return passage 27C.

[0069] A number of balls 30 are loaded into each of the ball circulatingpassages, each of which consists of the ball rolling passage (26A, 26B,26C), the ball return passage (27A, 27B, 27C), and the upper curvedpassage (29A, 29B, 29C).

[0070] The construction including the ball rolling passages 26A, 26B and26C, provided between the guide rail 21 and the slider 22, will bedescribed with reference to FIG. 7. In the upper ball rolling passage26A, the ball rolling groove 23A of the guide rail is disposed whilealigning with and facing the ball rolling groove 25A of the slider. Inthe medium ball rolling passage 26B, the ball rolling groove 23B of theguide rail is disposed facing the ball rolling groove 25B of the sliderin a state that the center of the ball rolling groove 25B is shifteddownward slightly or by an offset 6 with respect to the center of theball rolling groove 23B. In the lower ball rolling passage 26C, the ballrolling groove 23C of the guide rail is disposed facing the ball rollinggroove 25C of the slider in a state that the center of the ball rollinggroove 25C is shifted downward slightly by an offset 8 with respect tothe center of the ball rolling groove 23C.

[0071] Within the upper ball rolling passage 26A, each ball contacts atpoints T1 and T3 with the surface of the ball rolling groove 25A of theslider, and at points T2 and T4 with the surface of the ball rollinggroove 23A of the guide rail. That is, the number of contact points ofthe ball within the upper ball rolling passage 26A is totally four,contact points T1 to T4. A line L1 connecting the contact points T3 andT4 of those four ones is prolonged obliquely and downward to the leg 24.Another line L4 connecting the contact points T1 and T2 is prolongedobliquely and downward to the center of the guide rail 21.

[0072] Within the medium ball rolling passage 26B, each ball 30 contactsat a point T1 with the ball rolling groove 25B of the slider and at apoint T2 with the ball rolling groove 23B of the guide rail. Within thelower ball rolling passage 26C, each ball contacts at a point T1 withthe ball rolling groove 25C and at a point T2 with the ball rollinggroove 23C. Thus, the number of contact points of the ball within eachof those passages is two, contact points T1 and T2. Lines L2 and L3connecting those contact points T1 and T2 are obliquely and upwardprolonged to the leg of the slider, and intersects the prolonged line L1connecting two contact points of those four contact points, and convergeat points O1 and O2, which are located outside the guide rail 21, asshown in FIG. 7.

[0073] Of those four prolonged lines, the upper prolonged lines L4,medium prolonged lines L2 and lower prolonged line L3 are parallel toone another.

[0074] When the slider 22 is moved relative to the guide rail 21 in thelengthwise direction, the balls 30 put in the upper ball rolling passage26A (26B, 26C) move, while rolling, in the same direction but at a speedslower than the moving speed of the slider 22, with the movement of theslider. The balls are picked up by ball pick-up portions S, which areformed in one of the end caps 28, as shown in FIG. 8. The ball pick-upportion S changes the advancing direction of the balls and lead them tothe curved passage 29A (29B, 29C), which are provided in the same end ofthe slider 22 as of the end cap. Subsequently, the balls advance throughthe ball return passages 27A (27B and 27C) and the curved passage 29A(29B and 29C), which are provided on the opposite end to the endincluding the curved passages through which the balls already passed,and return to the upper ball rolling passage 26A (26B, 26C), andcontinue their advancing movement while tracing the same route.

[0075] The relationship between the direction of a load applied to and arigidity of the linear guide assembly will be described hereunder.

[0076] The prolonged line L1, and the prolonged lines L2 and L3 convergeat points O1 and O2 outside the guide rail 21. As stated above, theprolonged line L1 connects at the contact points T3 and T4 within theupper ball rolling passage 26A defining the four contact points relativeto the associated balls, and the prolonged lines L2 and L3 connect atthe contact points T1 and t2 within the medium and lower ball rollingpassages 26B and 26C defining the two contact points relative to theassociated balls, respectively.

[0077] The prolonged line L4, and the prolonged lines L2 and L3 areparallel to one another. When a force F acts on the linear guideassembly in the compressing direction as shown in FIG. 7(b), all theballs within the upper, medium and lower ball rolling passages 26A, 26Band 26C receive a load PF in share. Therefore, the linear guide assemblyexhibits a large rigidity against the load F acting downward. Thus, thelinear guide assembly having the three rows of ball rolling passagesexhibits its maximum load capacity against the force F acting in thecompressing direction.

[0078] When a load f acts on the slider 22 in the upward direction, theballs 30 within the upper ball rolling passage 26A receive the load Pfalong the prolonged line L1 connecting the contact points T3 and T4. Inthis state, the linear guide assembly exhibits a rigidity against theload Pf.

[0079]FIG. 9 is an engaged view showing a structure of ball rollingpassages in a linear guide assembly according to a second embodiment ofthe present invention.

[0080] In the embodiment, each the balls 30 contacts at two contactpoints T1 and T2 with the groove surfaces within each of the upper andmedium ball rolling passages 26A and 26B. Within the lower ball rollingpassage 26C, each ball 30 contacts at four contacts point T1 and T3, andT2 and T4 with the groove surfaces.

[0081] A prolonged line L1 connects the two contact points T1 and T2within the upper ball rolling passage 26A. A prolonged line L2 connectstwo contact points T1 and T2 within the medium ball rolling passage 26B.A prolonged line L4 connecting the contact points T1 and T2 within thelower ball rolling passage 26C. As stated above, each ball contacts atfour contact points T1 to T4 with the groove surfaces within the lowerball rolling passage 26C. These prolonged lines L1, L2 and L4 areextended obliquely and downward to inside the guide rail 21, while beingparallel to one another. A prolonged line L3 connects the contact pointsT3 and T4 with the groove surfaces within the lower ball rolling passage26C. The prolonged line L3 extends obliquely upward to inside the guiderail 21. The prolonged line L3, and the prolonged lines L1 and L2converge at points O1 and O2 inside the guide rail 21.

[0082] Also in this embodiment, if a load F acts on the upper surface ofthe slider 22 downward or in the compressing direction as shown in FIG.8(b), all the balls 30 within the upper, medium and lower ball rollingpassages 26A, 26B and 26C receive a load PF in share, and exhibits amaximum compressing load capacity, as a linear guide assembly havingthree rows of ball rolling passages.

[0083] When a load f acts upward on the slider 22, the balls 30 withinthe lower ball rolling passage 26C receive a load Pf along the prolongedline L3 connecting the contact points T3 and T4, and exhibits a rigidityagainst the load.

[0084]FIG. 9 is an engaged view showing a structure of ball rollingpassages in a linear guide assembly according to a third embodiment ofthe present invention.

[0085] In the third embodiment, as in the first embodiment, each ball 30contacts at four points with the groove surfaces within the upper ballrolling passage 26A. Within the medium and lower ball rolling passages26B and 26C, each ball contacts at two contact points with the groovesurfaces. The third embodiment is different from the first embodiment inthat in each of the medium and lower ball rolling passages 26B and 26C,the offset between the ball rolling grooves of the guide rail and theslider is opposite in direction to the offset between them in the firstembodiment.

[0086] A prolonged line L2 connects the contact points T1 and T2 of theball 30 within the medium ball rolling passage 26B. A prolonged line L3connects the contact points T1 and T2 within the lower ball rollingpassage 26C. A prolonged line L4 connects the contact points T3 and T4within the upper ball rolling passage 26A. Those prolonged lines L2, L3and L4 are extended obliquely upward to inside the guide rail 21, whilebeing parallel to one another. A prolonged line L1-connects the contactpoints T1 and T2 within the upper ball rolling passage 26A. Theprolonged line L1 is extended obliquely downward to inside the guiderail 21. The prolonged line L1, and the prolonged lines L2 and L3converge at points O1 and O2 inside the guide rail 21.

[0087] With such a construction, when a force f acts upward (in tensiledirection) on the slider 22 as shown in FIG. 9(b), all the balls 30receive a load Pf in share within the upper, medium and lower ballrolling passages 26A, 26B and 26C. Thus, the linear guide assemblyhaving the three rows of ball rolling passages exhibits a maximum ofload capacity against the load.

[0088] When a load F acts downward on the slider 22, the balls 30 withinthe upper ball rolling passage 26A receive a load PF along the prolongedline L1 connecting the contact points T1 and T2, and exhibits a rigidityagainst the load.

[0089]FIG. 10 is an engaged view showing a structure of ball rollingpassages in a linear guide assembly according to a fourth embodiment ofthe present invention.

[0090] In the fourth embodiment, as in the second embodiment, each ofthe balls 30 contacts at four points with the groove surfaces within thelower ball rolling passage 26C, and contacts at two points with thegroove surface within the upper and medium ball rolling passages 26A and26B. The fourth embodiment is different from the second embodiment inthat in each of the upper and medium ball rolling passages 26B and 26C,the offset between the ball rolling grooves of the guide rail and theslider is opposite in direction to the offset between them in the firstembodiment.

[0091] As shown, a prolonged line L1 connects the two contact points T1and T2 within the upper ball rolling passage 26A. A prolonged line L2connects the two contact points T1 and T2 within the medium ball rollingpassage 26B. A prolonged line L4 connects the contact points T1 and T2within the lower ball rolling passage 26C. As stated above, each ballcontacts at four contact points T1 to T4 with the groove surfaces withinthe lower ball rolling passage 26C. These prolonged lines L1, L2 and L4are extended obliquely downward to outside the guide rail 21 (the leg ofthe guide rail 21), while being parallel to one another. A prolongedline L3 connects the contact points T3 and T4 with the groove surfaceswithin the lower ball rolling passage 26C. The prolonged line L3 extendsobliquely and upward to outside the guide rail 21. The prolonged lineL3, and the prolonged lines L1 and L2 converge at points O1 and O2outside the guide rail 21.

[0092] In the present embodiment, when a force f acts upward (in tensiledirection) on the slider 22 as shown in FIG. 10(b), all the balls 30receive a load Pf in share within the upper, medium and lower ballrolling passages 26A, 26B and 26C. Thus, the linear guide assemblyhaving the three rows of ball rolling passages exhibits its maximum loadcapacity against the load.

[0093] When a load F acts downward on the slider 22, the balls 30 withinthe lower ball rolling passage 26C receive a load PF along the prolongedline L3 connecting the contact points T3 and T4, and exhibits a rigidityagainst the load.

[0094] A behavior of the linear guide assembly when a turning/rollingmoment M acts on the slider 22 will be described.

[0095] When a turning/rolling moment M (moment causing a rolling of theslider) acts on the slider 22, the linear guide assembly takes differentbehaviors when the intersection points O1 and O2 of the prolonged linesL1, L2 and L3 are present inside and outside the guide rail 21.Incidentally, those lines connect the contact points T1 and T2, and T3and T4 of the balls 30 with the groove surfaces within the upper, mediumand lower ball rolling passages 26A, 26B and 26C, as already stated.

[0096] In the linear guide assembly of the fourth embodiment of FIG. 10in which the intersection points O1 and O2 are outside the guide rail21, when a turning/rolling moment M is applied to the slider, loads areapplied to the balls 30 within the upper, medium and lower ball rollingpassages 26A, 26B and 26C, in the direction as shown in FIG. 11.

[0097] In the linear guide assembly of the third embodiment of FIG. 9 inwhich the intersection points O1 and O2 are inside the guide rail 21,when a turning/rolling moment M is applied to the slider, loads areapplied to the balls 30 within the upper, medium and lower ball rollingpassages 26A, 26B and 26C, in the direction as shown in FIG. 12.

[0098] When the intersection points O1 and O2 are outside the guide rail(FIG. 11), the vectors of loads PM1, PM2 and PM3, which are applied tothe balls 30 within the upper, medium and lower ball rolling passages26A, 26B and 26C of the left leg of the slider, are spaced apart, longdistances l1, l2 and l3, from the vector of a load PM4, which is appliedto the balls within the ball rolling passages in the right-hand leg.Therefore, the linear guide assembly exhibits large rigidity against aslant (rolling) of the slider 22 caused by the turning/rolling moment M.

[0099] When the intersection points O1 and O2 are inside the guide rail21 (FIG. 12), the vectors of the loads PM1, PM2 and PM3, which areapplied to the balls 30 within the upper, medium and lower ball rollingpassages 26A, 26B and 26C of the left-hand leg of the slider, are spacedapart, short distances l1, l2 and l3, from the vector of a load PM4,which is applied to the balls within the ball rolling passages in theright-hand leg. Therefore, the rigidity of the linear guide assembly issmall against a slant (rolling) of the slider 22 caused by theturning/rolling moment M. Therefore, in mounting the slider 22 on theguide rail 21, even if there is a mounting error, the linear guideassembly exercises the self-aligning function to absorb the error if itis within a tolerable range.

[0100] Thus, in the linear guide assembly where the intersection points(converging points) of the prolonged lines connecting the contact pointswith the groove surfaces within those ball rolling passages are insidethe guide rail, the slider has a large elastic displacement in themoment direction when the linear guide assembly receives a moment loadto roll the slider. Therefore, the linear guide assembly exercises theself-aligning function. On the other hand, when the intersection pointsare outside the guide rial, the rigidity of the linear guide assembly islarge against the moment load.

[0101] As seen from the foregoing description, in the linear guideassembly of the present invention, in the upper or lower load ballrolling passage of those three rows of ball rolling passages formed ineach side of the guide rail, each of the balls contacts, at four points,with the surfaces of the ball rolling grooves. In the remaining two ballrolling passages, each of the balls contacts, at two points, with thesurfaces of the ball rolling grooves. One of the prolonged lines eachconnecting opposite contact points of those four contact points of eachball in the upper or lower ball rolling passage is oriented in the samedirections as of the prolonged lines each connecting the two contactpoints of each ball in the remaining ball rolling passages. Therefore,all loads acting on the slider are received in share by three rows ofballs, viz., the balls within the three upper, medium and lower ballrolling passages. The linear guide assembly displays its maximum loadcapacity against the loads.

[0102] The prolonged lines, each of which connects the contact pointswhere each ball contacts with the surfaces of the ball rolling grooves,converge at points located inside or outside the guide rail. Therefore,when the linear guide assembly receives a turning/rolling moment (momentload) in the direction orthogonal to the lengthwise direction of theguide rail, the linear guide assembly exhibits a high rigidity againstthe moment load. With the improvement of the load capacity and therigidity of the linear guide assembly, the resultant linear guideassembly has a longer lifetime than the conventional one of the samesize. The linear guide assembly may be reduced in size while keeping itsrigidity and lifetime in satisfactory levels. When those lines convergeat points inside the guide rail, an self-aligning function of the linearguide assembly is exercised to absorb a mounting error, which is createdin assembling the linear guide assembly.

[0103] Thus, the present invention succeeds in providing an linear guideassembly whose the rigidity and self-aligning function are in practicallevels, while those of the conventional linear guide assembly are inunsatisfactory levels.

[0104]FIGS. 13 through 16 cooperatively show a fifth embodiment of thepresent invention. FIG. 13 is a front view of the linear guide assemblyin which the right half of the end cap is removed. FIG. 14 is a crosssectional view taken on line XIV-XIV in FIG. 13. FIG. 15 is an enlargedview typically showing one of load ball rolling passages. Theconstruction of the linear guide assembly will first be described. Asshown, a sliding block 112, shaped like U in cross section, is put abovea guide rail 111 such that the guide rail 111 and the sliding block 122move relative to each other. Three rows of ball rolling grooves, orupper, medium and lower ball rolling grooves 113A, 113B and 113C, whilelongitudinally extending, are formed in each side of the guide rail 111.The cross section of each ball rolling groove is shaped like a pointedarch, called a Gothic arch, having two centers and equal curvatures.Relief grooves 113 a, 113 b, and 113 c, which are provided for ballholders H, are formed in the bottoms of the ball rolling grooves 113A,113B and 113C, respectively, while being extended in the longitudinaldirection.

[0105] Ball rolling grooves 115A, 115B and 115C, while being verticallyarrayed, are formed in the inner surface of each of the legs 114 of ablock body 112A of the sliding block 112. The ball rolling groove 115Ais disposed in opposition to the upper ball rolling groove 113A of theguide rail to thereby form a ball rolling passage 116A; The ball rollinggroove 115B is disposed in opposition to the medium ball rolling groove113B to thereby form a ball rolling passage 116B; The ball rollinggroove 115C is disposed in opposition to the lower ball rolling groove113C to thereby form a ball rolling passage 116C. Ball return passages117A, 117B and 117C, circular in cross section, are formed in the thickpart of each of the legs 114 of the block body 112A, while beingvertically arrayed and, extending lengthwise and parallel respectivelyto the upper, medium and lower ball rolling passages 116A, 116B and116C.

[0106] Three halved-doughnut shaped, curved passages, or upper, mediumand lower curved passages 119A, 119B and 119C, are formed in each of endcaps 118 that are applied to the front and rear ends of the block body112A. The upper curved passage 119A interconnects the ball rollingpassage 116A and the ball return passage 117A; The medium curved passage119B interconnects the ball rolling passage 116B and the ball returnpassage 117B; The lower curved passage 119C interconnects the ballrolling passage 116C and the ball return passage 117C.

[0107] A number of balls 30 are loaded into each of the ball circulatingpassages, each of which consists of the ball rolling passage (116A,116B, 116C), the ball return passage (117A, 117B, 117C), and the uppercurved passage (119A, 119B, 119C).

[0108] The construction including the upper, medium lower ball rollingpassages 116A, 116B and 116C, provided between the guide rail 111 andthe sliding block 112, will be described with reference to FIG. 15. Inthe upper, medium and lower ball rolling passages 116A to 116C, the ballrolling grooves 113A to 113C of the guide rail are respectively disposedfacing the ball rolling grooves 115A to 115C of the sliding block whilebeing on a level with the latter. With such a construction, the balls120 within the ball circulating passages 116A to 116C contact at pointsT1 and T3 with the surfaces-of the ball rolling grooves 115A to 115C ofthe sliding block 112, and at points T2 and T4 with the surfaces of theball rolling grooves 113A to 113C of the guide rail 111. Thus, the ballscontact at four points with the groove surfaces in all the upper, mediumand lower ball rolling passages 116A, 116B and 116C.

[0109] The operation of the linear guide assembly thus constructed willbe described.

[0110] When the sliding block 112 is moved above and along the guiderail 111 in the axial direction, the balls 120 put in the ballcirculating passage 116A (116B, 116C) move, while rolling, at a speedlower than the sliding block 112 in the same direction as of themovement of the sliding block. At the extreme end of the moving path ofthe sliding block 112, the balls are led to the ball pick-up portion S,which is provided at one of the end caps 118. In the ball pick-upportion S, their advancing direction is changed, and the balls advancealong the upper curved passage 119A (119B, 119C) where the balls are Uturned in their advancing direction. In turn, the balls advance in andalong the ball return passage 117A (117B, 117C) of the block body 112Aand enter the upper curved passage 119A (119B, 119C) of the other endcap 118. By the end cap, the balls are U turned in their advancingdirection and return to the ball circulating passage 116A (116B, 116C).Subsequently, such a circulating movement of the balls is repeated.

[0111] The relationship between the load direction and rigidity of thelinear guide assembly will be described.

[0112] When a force F of the compression direction acts on the uppersurface of the sliding block 112 as shown in FIG. 15, the balls 120 inthe upper, medium and lower ball rolling passages 116A, 116B and 116Creceive a load PF in share in the directions of lines connecting thecontact points T1 and T2. Therefore, the linear guide assembly of thethree rows of ball sliding grooves exhibits its maximum load capacityand the largest rigidity against the force F acting thereon.

[0113] When a tensile load f acts upward on the sliding block 112 asshown in FIG. 16, the balls 120 in the upper, medium and lower ballrolling passages 116A, 116B and 116C receive a load Pf in share. In thiscase, the balls receive the load in share in the directions of linesconnecting contact points T3 and T4.

[0114] In the fifth embodiment, the balls 120 in all the upper, mediumand lower ball rolling passages 116A, 116B and 116C receive the loadapplied to the sliding block 112 in share independently of the directionof the load. Therefore, the linear guide assembly always exhibits itsmaximum load capacity and the largest rigidity against the force Facting thereon.

[0115] A sixth embodiment of the present invention will be describedwith reference to FIGS. 17 and 18.

[0116] The sixth embodiment is different from the fifth embodiment inthat, in the upper ball circulating passage 116A, the ball rollinggroove 113A of the guide rail 111, each being shaped like a 1/4(quarter) arc in cross section,-is formed at the corner (ridge) of theguide rail, and that within the ball circulating passage 116A each ball120 contacts at two points T1 and T2 with the groove surfaces.

[0117] In the medium and lower ball rolling passages 116B and 116C, theballs 120 contact with the groove surfaces, at four points T1, T3, andT2, T4.

[0118] In the present embodiment, when a compression load F actsdownward on the upper surface of the sliding block 112 as shown in FIG.17, the balls receive the load PF in share in the directions of linesconnecting the contact points T1 and T2 in all the upper, medium andlower ball rolling passages 116A, 116B and 116C. Therefore, the linearguide assembly displays its maximum load capacity and high rigidityagainst the compression load. Further, on the ball rolling grooves 113Aand 115A of the upper ball circulating passage 116A, rolling resistanceof the balls is low because those balls contact at two contact pointswith the groove surfaces.

[0119] When a tensile load f acts upward on the sliding block 112, theballs on the ball rolling grooves of the medium and lower ball rollingpassages 116B and 116C receive the tensile load in share along the linesconnecting the contact points T3 and T4, but the balls on the ballrolling grooves of the upper ball circulating passage 116A does notreceive the tensile load f.

[0120] A seventh embodiment of the present invention will be describedwith reference to FIGS. 19 and 20.

[0121] The seventh embodiment is different from the fifth and sixthembodiments in that the balls 120 in the upper and medium ballcirculating passage 116A and 116B are brought into contact with thegroove surfaces at four points T1 to T4, and the balls 120 in the lowerball rolling passage 116C are in contact with the groove surfaces at twopoints T3 and T4. In the lower ball rolling passage 116C, the balls 120are each in contact with the groove surfaces at two points in a statethat the ball rolling groove 115C of the sliding block 112 are shiftedupward by a short distance or an offset δ, with respect to the lowerball rolling groove 113C of the guide rail 111.

[0122] When a tensile load f acts upward on the upper surface of thesliding block 112 as shown in FIG. 20, the balls in the upper, mediumand lower ball rolling passages 116A, 116B and 116C receive the load Pfin share along the lines connecting the contact points T3 and T4.Therefore, the linear guide assembly exhibits its maximum load capacityand the largest rigidity when it receives the tensile load f. Further,on the ball rolling grooves 113A and 115A of the upper ball circulatingpassage 116A, rolling resistance of the balls is low because those ballsare in contact with the groove surfaces at two contact points.

[0123] When the compression load acts downward on the sliding block 112,the balls 120 in the upper and medium ball circulating passages 116A and116B receive the load in share along the lines connecting the contactpoints T1 and T2. At this time, the balls 120 in the lower ball rollingpassage 116C do not receive the load.

[0124] In the present embodiment, in the lower ball rolling passage116C, the ball rolling groove 115C of the sliding block 112 is shiftedupward, by the offset 6, with respect to the lower ball rolling groove113C of the guide rail ill. With presence of the offset, the lineconnecting the two contact points of each ball in the lower ball rollingpassage 116C is changed to be parallel to the lines connecting thecontact points T1 and T2 in the remaining ball rolling passages.Therefore, when a compression force F acts on the sliding block 112, theballs 120 of the upper, medium and lower ball rolling passages 116A,116B and 116C receive the load PF in share. Hence, the linear guideassembly exhibits its maximum load capacity.

[0125] A eighth embodiment of the present invention will be describedwith reference to FIGS. 21 and 22.

[0126] The eighth embodiment is different from the fifth to seventhembodiments in that in the upper and lower ball circulating passages116A and 116C each ball contact with the groove surfaces at four pointsT1 to T4, and in the medium ball rolling passage 116B each ball contactwith the groove surfaces at two points T1 and T2. In the medium ballrolling passage 116B, each ball 120 contacts with the groove surfaces attwo points in a state that the ball rolling groove 115B of the slidingblock 112 is shifted downward slightly or by an offset 8, with respectto the medium ball rolling groove 113B of the guide rail 111.

[0127] When a compression force F acts downward on the upper surface ofthe sliding block 112 as shown in FIG. 22, the balls receive the load PFin share in the direction of the lines connecting the contact points T1and T2 on the ball rolling grooves of all the upper, medium and lowerball rolling passages 116A, 116B and 116C. Therefore, the linear guideassembly exhibits its maximum load capacity against the compression loadapplied thereto. Further, each ball contacts at two points with themedium ball rolling grooves 113B and 115B of the medium ball rollingpassage 116B, and hence the rolling resistance of the balls is small.

[0128] When a tensile load acts upward on the sliding block 112, theballs 120 on the ball rolling grooves of the upper and lower ballcirculating passages 116A and 116C receive the load in share along thelines connecting the contact points T3 and T4. At this time, the balls120 on the ball rolling grooves of the medium ball rolling passage 116Bdo not receive the compression load.

[0129] In the present embodiment, in the medium ball rolling passage116B, the ball rolling groove 115B of the sliding block 112 is shiftedupward slightly or by an offset 6, with respect to the lower ballrolling groove 113B of the guide rail 111. With presence of the offset,the line connecting the two contact points of each ball in the mediumball rolling passage 116B is changed to be parallel to the linesconnecting the contact points T3 and T4 in the remaining ball rollingpassages. Therefore, when a tensile load f acts on the sliding block112, the balls 120 of the upper, medium and lower ball rolling passages116A, 116B and 116C receive the load Pf in share, and the linear guideassembly exhibits its maximum load capacity.

[0130] A contact angle at which each ball 120 contacts with the surfacesof the ball rolling groove 113B of the guide rail 111 and the ballrolling groove 115B in the medium ball rolling passage 116B may be setat 0° as shown in FIG. 23 (In this case, the ball rolling grooves areeach arcuate in cross section, and oppositely disposed while the centersof the grooves are horizontally aligned with each other, although thegrooves are each shaped like a Gothic arch in cross section andoppositely disposed while the centers of the grooves are horizontallyshifted one from the other.).

[0131] The linear guide assembly thus constructed has the increased loadcapacity and rigidity against the load F acting on the side of thesliding block 112.

[0132] As seen from the foregoing description, in the linear guideassembly of the invention, in all the three rows of ball rollingpassages, the balls are brought into contact with the surfaces of theball rolling grooves at four points. The upper, medium and lower trainsof balls receive all the loads acting on the sliding block in share.Therefore, the linear guide assembly displays its maximum load capacityand high rigidity against the loads independently of the directions ofthe loads.

[0133] The balls are brought into contact, at four points, with thegroove surfaces in at least two ball circulating passages, whereby thelinear guide assembly is capable of bearing loads in every direction.The remaining ball circulating passage are arranged such that each balltherein is in contact, at two points, with the groove surfaces, inconsideration with the direction of the load applied to the slidingblock. Therefore, the balls on all the ball rolling grooves are fullyutilized, and the load capacity and the rigidity may be selected to beas large as possible so long as the rolling resistance of the balls arenot increased, in accordance with the direction of the load appliedthereto.

[0134] Since the load capacity and the rigidity of the linear guideassembly are thus increased, the resultant linear guide assembly has alonger lifetime when comparing with the linear guide assembly of thesame size as of the former. Besides, the linear guide assembly may bereduced in size and in the number of sliding blocks while keeping therequired rigidity and lifetime.

[0135]FIGS. 24 through 26 cooperatively show a ninth embodiment of thepresent invention. FIG. 24 is a side view of the linear guide assemblyin which the right side of the end cap is removed. FIG. 25 is a crosssectional view taken on line XXV-XXV in FIG. 24. FIG. 6 is an enlargedview typically showing one of load ball rolling passages. Theconstruction of the linear guide assembly will first be described. Asshown, a sliding block 202, shaped like U in cross section, is put abovea guide rail 201 such that the guide rail 201 and the sliding block 202move relative to each other. Three rows of ball rolling grooves, orupper, medium and lower ball rolling grooves 203A, 203B and 203C, whilelongitudinally extending, are formed in each side of the guide rail 201.The upper and lower ball rolling grooves 203A and 203C are arcuate incross section. The medium ball rolling groove is shaped, in crosssection, like a pointed arch, called a Gothic arch, having two centersand equal curvatures.

[0136] Ball rolling grooves 205A, 205B and 205C, while being verticallyarrayed, are formed in the inner surface of each of the legs 204 of ablock body 202A of the sliding block 202. The ball rolling groove 205Ais disposed in opposition to the upper ball rolling groove 203A of theguide rail to thereby form a ball rolling passage 206A; The ball rollinggroove 205B is disposed in opposition to the medium ball rolling groove203B to thereby form a ball rolling passage 206B; The ball rollinggroove 205C is disposed in opposition to the lower ball rolling groove203C to thereby form a ball rolling passage 206C. Those opposed ballrolling groove pairs form upper, medium and lower ball rolling passages206A, 206B and 206C, respectively.

[0137] Ball return passages 207A, 207B and 207C, circular in crosssection, are formed in the thick part of each of the legs 204 of theblock body 202A, while being vertically arrayed and, respectively,extending lengthwise and parallel to the upper, medium and lower ballrolling passages 206A, 206B and 206C.

[0138] Three halved-doughnut shaped, curved passages, or upper, mediumand lower curved passages 209A, 209B and 209C, are formed in each of endcaps 208 that are applied to the front and rear ends of the block body202A. The upper curved passage 209A interconnects the ball rollingpassage 206A and the ball return passage 207A; The medium curved passage209B interconnects the ball rolling passage 206B and the ball returnpassage 207B; The lower curved passage 209C interconnects the ballrolling passage 116C and the ball return passage 207C.

[0139] A number of balls 210 are loaded into each of the ballcirculating passages, each of which consists of the ball rolling passage(206A, 206B, 206C), the ball return passage (207A, 207B, 207C), and thecurved passage (209A, 209B, 209C).

[0140] The construction including the upper, medium lower ball rollingpassages 206A, 206B and 206C, provided between the guide rail 201 andthe sliding block 202, will be described with reference to FIG. 26.

[0141] The upper ball rolling passage 206A is formed by a combination ofgrooves, each arcuate in cross section. In the passage, the ball 210contacts, at two points, with the surfaces of the grooves. A groove Rratio of the flank 203 f of the ball rolling groove 203A of the guiderail is set at R1. A groove R ratio of the flank 205 f of the ballrolling groove 205A of the sliding block is also set at R1. The ballrolling groove 205A is slightly shifted downward with respect to theball rolling groove 203A. The ball 210 contacts with the surfaces ofthose grooves at points T1 and T2.

[0142] The lower ball rolling passage 206C is formed by a combination ofgrooves, each arcuate in cross section. In the passage, the ball 210contacts, at two points, with the surfaces of the grooves. A groove Rratio of the flank 203 f of the ball rolling groove 203C of the guiderail is set at R1. A groove R ratio of the flank 205 f of the ballrolling groove 205C of the sliding block is also set at R1. The ballrolling groove 205C is slightly shifted upward with respect to the ballrolling groove 203C. The ball 210 contacts with the surfaces of thosegrooves at points T3 and T4.

[0143] The medium ball rolling passage 206B is formed by a combinationof grooves, each having the form of a Gothic arch in cross section. Inthe passage, the ball 210 contacts, at four points, with the surfaces ofthe grooves. The ball rolling groove 203B of the guide rail takes theform of a Gothic arch in cross section, viz., the cross section of it isshaped like V defined by an arcuate flank 203fl of the groove R ratio R2and an arcuate flank 203 f 2 of the groove R ratio R2. The centers ofthose flanks are not coincident with each other. The ball rolling groove205B of the sliding block takes the form of a Gothic arch in crosssection, viz., the cross section of it is shaped like V defined by anarcuate flank 205fl of the groove R ratio R2 and an arcuate flank 205 f2 of the groove R ratio R2. The centers of those flanks are notcoincident with each other. Those grooves are confronted with each otherwhile the centers of them being on the same level. The ball 210 contactswith those grooves at four points T1, T2, T3 and T4.

[0144] For the ball rolling grooves 203A and 205A, and 203C and 205C ofthe ball rolling passages 206A and 206C of the two contact points, aratio (groove R ratio) of the curvature radius R1 of the flank (203 f,205 f) to the diameter of the ball 210 is set at a value being more than50% but less than 53%.

[0145] For the ball rolling grooves 203B and 205B of the ball rollingpassages 206B of the four contact points, a ratio (groove R ratio) ofthe curvature radius R2 of the flank (203fl, 203 f 2, and 205fl, 205 f2) to the diameter of the ball 210 is set at a value within a range from53% to 56%.

[0146] The operation of the linear guide assembly thus constructed willbe described.

[0147] When the sliding block 202 is moved above and along the guiderail 201 in the axial direction, the balls 210 put in the ballcirculating passage 206A (206B, 206C) move, while rolling, at a speedlower than the sliding block 202 in the same direction as the movingdirection of the sliding block. At the end of the moving path of thesliding block 202, the balls are led to the ball pick-up portion S,which is provided at one of the end caps 208. By the ball pick-upportion S, their advancing direction is changed, and the balls advancealong the upper curved passage 209A (209B, 209C) where the balls arereturned in their advancing direction. In turn, the balls advance in andalong the ball return passage 207A (207B, 207C) of the block body 202Aand enter the upper curved passage 209A (209B, 209C) of the other endcap 208. By the end cap, the balls are returned in their advancingdirection and return to the ball rolling passage 206A (206B, 206C).Subsequently, such a circulating movement of balls is repeated.

[0148] The relationship between the groove structure of the ball rollinggrooves and the load capacity of the linear guide assembly will bedescribed.

[0149] Each ball 210 in the medium ball rolling passage 206B receives aload in a state that it contacts with the surfaces of the ball rollinggrooves 203B and 205B at four points T1, T2, T3 and T4. The groove Rratio of each of the ball rolling grooves 203B and 205B is between 53%and 56%, approximately equal to the value of the groove R ratio of theball rolling groove of the conventional linear guide assembly.Therefore, there is no increase of the rolling friction of the ball, andthere is no chance that a small error of the contact angle greatlyaffects the characteristics of the linear guide assembly, making itdifficult to control the accuracy of the groove forming.

[0150] In the upper ball rolling passage 206A, each ball 210 receives aload in a state that it contacts, at two points T1 and T2, with thesurfaces of the ball rolling grooves 203A and 205A. Also the lower ballrolling passage 206C, each ball 210 receives a load in a state that itcontacts, at two points T3 and T4, with the surfaces of the ball rollinggrooves 203C and 205C. The rolling friction of the ball contacting attwo points with the groove surfaces is originally small. Therefore, evenif the curvature radius is reduced to be small, an increase of therolling friction is not so much. In this case, the load capacity andrigidity are increased.

[0151] The present embodiment succeeds in increasing the load capacityand rigidity, while keeping easy working of grooves and easy control ofworking accuracy and little increasing the rolling friction of theballs.

[0152] As seen from the foregoing description, in the invention, of thethree rows of ball rolling passages formed on each side of the linearguide assembly, only one row of ball rolling passage is arranged suchthat each ball contacts, at four contact points, with the groovesurfaces. The groove R ratio of the groove flank is approximately equalto that of the groove R ratio generally used. The remaining two ballrolling passages are arranged such that each ball contacts, at twopoints, with the groove surfaces. A groove R ratio of the groove of eachof those ball rolling passages of the two contact points is set to besmaller than that of the ball rolling passage of the four contactpoints. Therefore, the linear guide assembly of the invention is freefrom the problems of the error of the contact angle owing to the workingaccuracy and the increase of the rolling friction. The load capacity andrigidity of the linear guide assembly are increased. Thus, the presentembodiment can increase the load capacity and rigidity, while keepingeasy working of grooves and easy control of working accuracy and littleincreasing the rolling friction of the balls.

[0153] While there has been described in connection with the preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is aimed, therefore, to cover inthe appended claim all such changes and modifications as fall within thetrue spirit and scope of the invention.

What is claimed is:
 1. A linear guide assembly comprising: a guide railhaving three rows of ball rolling grooves on each side thereof; a sliderslidably mounted on said guide rail, said slider having legs extendingalong both sides of the guide rail, each of the legs of the sliderincluding three rows of ball rolling grooves respectively disposed inopposition to said three rows of said ball rolling grooves of said guiderail so as to define three rows of ball rolling passages therebetween,said slider being provided with a number of ball circulating passageseach containing said respective ball rolling passages; and a number ofballs being put in each of said ball circulating passages; wherein saidthree rows of ball rolling passages are constituted by an upper, mediumand lower ball rolling passages, and each balls put in one of said upperand lower ball rolling passage contacts at four points with the surfacesof said ball rolling grooves of said guide rail and said slider, whileeach balls put in the remaining two ball rolling passages contacts attwo points with the surfaces of the ball rolling grooves of said guiderail and said slider, and wherein one of lines defined by connecting thetwo opposite contact points of those four contact points of said one ofupper and lower ball rolling passages, and lines defined by connectingrespectively the two opposite contact points of the remaining two ballrolling passages are intersected at points which are located inside oroutside said guide rail.
 2. The linear guide assembly according to claim1, in which in said medium ball rolling passage, the ball rolling grooveof said guide rail is disposed facing the ball rolling groove of saidslider in a state that the center of the ball rolling groove of saidslider is shifted downward a predetermined offset with respect to thecenter of said ball rolling groove of said guide rail, and in the lowerball rolling passage, the ball rolling groove of the guide rail isdisposed facing the ball rolling groove of the slider in a state thatthe center of the ball rolling groove of said slider is shifted downwardby a predetermined offset with respect to the center of the ball rollinggroove of said guide rail.
 3. The linear guide assembly according toclaim 1, in which in said medium ball rolling passage, the ball rollinggroove of said guide rail is disposed facing the ball rolling groove ofsaid slider in a state that the center of the ball rolling groove ofsaid slider is shifted downward a predetermined offset with respect tothe center of said ball rolling groove of said guide rail, and in theupper ball rolling passage, the ball rolling groove of the guide rail isdisposed facing the ball rolling groove of the slider in a state thatthe center of the ball rolling groove of said slider is shifted downwardby a predetermined offset with respect to the center of the ball rollinggroove of said guide rail.
 4. The linear guide assembly according toclaim 1, in which in said medium ball rolling passage, the ball rollinggroove of said guide rail is disposed facing the ball rolling groove ofsaid slider in a state that the center of the ball rolling groove ofsaid slider is shifted upward a predetermined offset with respect to thecenter of said ball rolling groove of said guide rail, and in the lowerball rolling passage, the ball rolling groove of the guide rail isdisposed facing the ball rolling groove of the slider in a state thatthe center of the ball rolling groove of said slider is shifted upwardby a predetermined offset with respect to the center of the ball rollinggroove of said guide rail.
 5. The linear guide assembly according toclaim 1, in which in said medium ball rolling passage, the ball rollinggroove of said guide rail is disposed facing the ball rolling groove ofsaid slider in a state that the center of the ball rolling groove ofsaid slider is shifted upward a predetermined offset with respect to thecenter of said ball rolling groove of said guide rail, and in the upperball rolling passage, the ball rolling groove of the guide rail isdisposed facing the ball rolling groove of the slider in a state thatthe center of the ball rolling groove of said slider is shifted upwardby a predetermined offset with respect to the center of the ball rollinggroove of said guide rail.
 6. The linear guide assembly according toclaim 1, in which each of said ball circulating passage comprises: oneof said ball rolling passages; a ball return passage extending inparallel with said ball rolling passages; and curved passages, one ofsaid curved passages interconnecting one ends of said one of said ballrolling passages and said ball return passage, while the otherinterconnecting the other ends of said one of said ball rolling passagesand said ball return passage.
 7. A linear guide assembly comprising: aguide rail having three rows of ball rolling grooves on each sidethereof; a slider slidably mounted on said guide rail, said sliderhaving legs extending along both sides of the guide rail, each of thelegs of the slider including three rows of ball rolling groovesrespectively disposed in opposition to said three rows of said ballrolling grooves of said guide rail so as to define three rows of ballrolling passages therebetween, said slider being provided with a numberof ball circulating passages containing said respective ball rollingpassages; and a number of balls being put in each of said ballcirculating passages; wherein each ball put in at least two rows of saidthree rows of said ball rolling passage contacts at four points with thesurfaces of said ball rolling grooves of said guide rail and saidslider, while each balls put in the remaining ball rolling passagecontacts at least two points with the surfaces of the ball rollinggrooves of said guide rail and said slider.
 8. The linear guide assemblyaccording to claim 7, in which said three rows of ball rolling passagesare constituted by an upper, medium and lower ball rolling passages, andsaid at least two rows of said three rows of said ball rolling passageare said medium and lower rolling passages.
 9. The linear guide assemblyaccording to claim 7, in which said three rows of ball rolling passagesare constituted by an upper, medium and lower ball rolling passages, andsaid at least two rows of said three rows of said ball rolling passageare said upper and medium rolling passages.
 10. The linear guideassembly according to claim 7, in which said three rows of ball rollingpassages are constituted by an upper, medium and lower ball rollingpassages, and said at least two rows of said three rows of said ballrolling passage are said upper and lower rolling passages.
 11. Thelinear guide assembly according to claim 7, in which each ballsrespectively put in said three ball rolling passages contacts at fourpoints with the surfaces of said ball rolling grooves of said guide railand said slider.
 12. The linear guide assembly according to claim 7, inwhich each of said ball circulating passage comprises: one of said ballrolling passages; a ball return passage extending in parallel with saidball rolling passages; and curved passages, one of said curved passagesinterconnecting one ends of said one of said ball rolling passages andsaid ball return passage, while the other interconnecting the other endsof said one of said ball rolling passages and said ball return passage.13. A linear guide assembly comprising: a guide rail having three rowsof ball rolling grooves on each side thereof; a slider slidably mountedon said guide rail, said slider having legs extending along both sidesof the guide rail, each of the legs of the slider including three rowsof ball rolling grooves respectively disposed in opposition to saidthree rows of said ball rolling grooves of said guide rail so as todefine three rows of ball rolling passages therebetween, said sliderbeing provided with a number of ball circulating passages containingsaid respective ball rolling passages; and a number of ball being put ineach of said ball circulating passages; wherein at least one row of saidthree rows of said ball rolling passages is arranged such that each ballcontacts, at four points, with the surfaces of said ball rolling groovesof said guide rail and said slider, while the remaining rows of saidball rolling passages are arranged such that each ball contacts, at twopoints, with the surfaces of said ball rolling grooves of said guiderail and said slider, and wherein a groove R ratio of the flanks of theball rolling grooves of each of remaining rows is more than 50% butsmaller than that of the flanks of the ball rolling grooves of said ballrolling passage where each ball contacts at four points with said groovesurfaces, where said groove R ratio defines a ratio of the radius ofcurvature of said flank to the diameter of said ball.
 14. The linearguide assembly according to claim 13, in which the groove R ratio of theflanks of the ball rolling grooves of each of said ball rolling passageswhere each ball contacts at two points with the groove surfaces, is morethan 50% but less than 53%, and the groove R ratio of the flanks of theball rolling grooves of said ball rolling passage where each ballcontacts at four points with the groove surfaces is in the range of53%-56%.
 15. The linear guide assembly according to claim 13, in whicheach of said ball circulating passage comprises: one of said ballrolling passages; a ball return passage extending in parallel with saidball rolling passages; and curved passages, one of said curved passagesinterconnecting one ends of said one of said ball rolling passages andsaid ball return passage, while the other interconnecting the other endsof said one of said ball rolling passages and said ball return passage.